The problem is you are still pending interview. Even if after the interview, they may take more time to interview other candidates. They might not even select you or let you know.

So it is best if you can call up HR right now and tell them that another company has offered you a job and see if they can get you an interview and let you know the results asap. If they are unable to do so, chances are you are not their first choice and you can safely accept the job offer.